The present invention relates to processing semiconductor wafers, especially for use in applications such as electronics, microelectronics, and optoelectronics. In particular, the invention pertains to an implantation process for a wafer that includes at least a layer having an uneven surface, wherein implanting occurs through the uneven surface.
It is known to employ implantation processes for semiconductor wafers to obtain various effects. For example, implantation can be used to create a weakened zone within the thickness of the wafer. The SMART-CUT® process is an example of an implantation method that produces a weakened zone. A general description of the SMART-CUT® process can be found, for example, in “Silicon-On-Insulator Technology: Materials to VLSI”, 2nd edition by Jean-Pierre Colinge, from Kluwer Academic Publishers, pages 50 and 51.
When a weakened zone is to be created in the thickness of the wafer, for example by using a layer transfer method such as a SMART-CUT® type process, it is generally preferred for the weakened zone to have an even surface that extends substantially in a plane. In general, for numerous implantation applications, it is desirable to implant species so that the implanted samples are evenly distributed in the thickness of the wafer at a particular implantation depth under the surface of the wafer. Implantation that occurs through an uneven surface adversely affects the uniformity of the depth of implantation of the samples. FIG. 1 illustrates this phenomenon. Referring to FIG. 1, samples have been implanted in a wafer 10 through a layer 12 of material having an uneven surface 120, and through a portion of the substrate 11 upon which the layer 12 is located. Due to the uneven character of the surface 120, the depth of implantation (shown by the line 13) is also uneven. This is a disadvantage.
In this text “uneven surface” means a surface having a roughness value that is greater than a value on the order of several angstroms in root mean square (rms) value. It should also be noted that in the present text an even surface is one that has a roughness value less than several angstroms rms.